The ability of soft materials, like block copolymers, to self-assemble into arrays of nanometer-sized domains makes them attractive candidates for the generation of high-density media for use in data storage, electronics, and molecular separation. See, e.g., T. Thurn-Albrecht et al., Science, volume 290, pages 2126-2129 (2000); H. J. Fan et al., Small, volume 2, pages 700-717 (2006); and M. J. Fasolka and A. M. Mayes, Annual Reviews of Materials Research, volume 31, pages 323-355 (2001). Block copolymers have gained increasing attention as templates and scaffolds for the fabrication of high-density arrays of nanoscopic elements due to the size and tunability of the microdomains, the ease of processing without introducing disruptive technologies, and the ability to manipulate their functionality. See, e.g., C. J. Hawker and T. P. Russell, MRS Bulletin, volume 30, pages 952-966 (2005); M. Li et al., Advances in Polymer Science, volume 190, pages 183-226 (2005); M. Park et al., Science, volume 276, pages 1401-1404 (1997); T. Thurn-Albrecht et al., Advanced Materials, volume 12, pages 787-791 (2000); and T. Xu et al., Advanced Functional Materials, volume 13, pages 698-702 (2003). For block copolymers having cylindrical microdomains with high aspect ratios, it is necessary to control the orientation and lateral ordering of the microdomains to optimize the contrast in transfer applications and the lateral density of elements. It is also highly desirable that the process be independent of the underlying substrate. Approaches to manipulate the orientation and lateral ordering of the microdomains in thin films of block copolymers include the use of solvent fields (see, e.g., G. Kim et al., Macromolecules, volume 31, pages 2569-2577 (1998); M. Kimura et al., Langmuir, volume 19, pages 9910-9913 (2003); S. Ludwigs et al., Nature Materials, volume 2, pages 744-747 (2003); and S. H. Kim et al., Advanced Materials, volume 16, pages 226-231 (2004)), electric fields (see, e.g., T. Thurn-Albrecht et al., Macromolecules, volume 33, pages 3250-3253 (2000)), chemically patterned substrates (see, e.g., M. P. Stoykovich et al., Science, volume 308, pages 1442-1446 (2005); S. O. Kim. et al., Nature, volume 424, pages 411-414 (2003)), graphoepitaxy (see, e.g., R. A. Segalman et al., Advanced Materials, volume 13, pages 1152-1155 (2001)), epitaxial crystallization (see, e.g., C. De Rosa et al., Nature, volume 405, pages 433-437 (2000)), controlled interfacial interactions (see, e.g., P. Mansky et al., Science, volume 275, pages 1458-1460 (1997); E. Drockenmuller et al., Journal of Polymer Science, Part A: Polymer Chemistry, volume 43, pages 1028-1037 (2005)), thermal gradients (see, e.g., J. Bodycomb et al., Macromolecules, volume 32, pages 2075-2077 (1999)), zone casting (see, e.g., C. Tang et al., Journal of the American Chemical Society, volume 127, pages 6918-6919 (2005)), and shear (see, e.g., M. A. Villar et al., Polymer, volume 43, pages 5139-5145 (2002)).
By removal of the minor (by volume) phase, a nanoporous template is produced where the aspect ratio of the pores is dictated by the thickness of the film. While the aspect ratio of the pores provides a natural etching contrast, the incorporation of an inorganic element, like Si or Fe into one of the blocks has also been used to enhance contrast. See, e.g., M. A. Hartney et al., Journal of Vacuum Science and Technology B, volume 3, pages 1346-1351 (1985); J. Y. Cheng et al., Applied Physics Letters, volume 81, pages 3657-3659 (2002); and K. Temple et al., Advanced Materials, volume 15, pages 297-300 (2003). As another example, Park et al. used an OsO4-stained microphase-separated thin film of poly(styrene-block-butadiene), which, with a reactive ion etch (RIE) contrast of 2:1, produced an array of holes in an underlying silicon nitride substrate. See M. Park et al., Science, volume 276, pages 1401-1404 (1997). And Spatz et al. quaternized poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) with auric acid, depositing gold in the P2VP microdomains, to generate masks for nanolithography. See J. P. Spatz et al., Advanced Materials, volume 11, pages 149-153 (1999). Spatz et al. have also “grown” Ti on top of a polystyrene matrix to enhance contrast. See J. P. Spatz et al., Advanced Materials, volume 10, pages 849-852 (1998).
Notwithstanding the variety of existing methods for using block copolymers to create nanoporous substrates, there remains a need for simplified methods that are applicable to a wide variety of substrates, avoid any requirement for complicated procedures to produce long-range order in the block copolymer film, and avoid any requirement for metal functionalization of the block copolymer.